Gross traded fraction is not a fund’s reported turnover ratio

Name the convention in the first sentence

A turnover percentage can mean gross trading, one-sided replacement or a published fund accounting measure. The SEC’s Form N-1A instructions describe a fund turnover calculation based on the lesser of purchases and sales, with specified denominators and exclusions. The workbench instead needs the dollars on which its modeled execution costs are incurred.

Accordingly, define gross traded fraction as the sum of absolute modeled order notionals divided by scenario AUM. A buy and a sell each contribute to trading activity. This convention is useful for execution-cost arithmetic but does not replace a fund’s required financial reporting methodology or support a direct comparison with every published turnover statistic.

A two-sided rebalance

Consider a hypothetical $20 million portfolio. It sells $2 million of one security and buys $2 million of another, with no other activity. Net cash movement is approximately zero before costs. Gross trading is $4 million, so gross traded fraction is 20%. One-sided replacement is 10%. A zero net-flow number would hide both execution legs.

At an assumed 10 bps per traded dollar on both legs, total modeled cost is $4 million × 0.001 = $4,000. Dividing by $20 million gives 2 bps of portfolio drag. Applying 10 bps only to the $2 million purchase would understate modeled costs by half. Applying 10 bps to all AUM would overstate them fivefold.

Translate sleeve fractions carefully

In this calculator, a 15% sleeve traded by 40% produces an order of 6% of AUM. A second 10% sleeve traded by 60% also produces 6% of AUM. Together they contribute 12% gross trading, regardless of whether their directions offset in net cash terms.

A position-level trade fraction describes how much of that sleeve changes in the modeled event. It is not automatically an annual turnover rate. If a sleeve is sold and later rebuilt, both events belong in the annual cost accounting. Preserve separate event records rather than forcing an annual history into a single ambiguous fraction.

Use consistent portfolio values

For an event scenario, a single specified AUM makes the arithmetic inspectable. For an empirical annual study, cash flows and market returns change the denominator. Choose a documented method, such as event-level cost divided by the portfolio value at each event, and explain how those event contributions are aggregated.

For example, a $1,000 trading cost on $10 million is 1 bp; the same dollars on $20 million are 0.5 bp. Combining two costs and dividing by the final portfolio value can distort the earlier contribution after a large subscription. A size comparison should separate changes in trading behavior from changes in the capital base.

Reconcile rather than relabel

An evidence pack should retain purchases, sales, gross notional, net cash flow, AUM convention and cost denominator as separate columns. If a third-party report supplies only a turnover percentage, ask for its definition before using it to forecast trading expense. A rounded headline cannot reveal whether derivatives, short-dated instruments or reinvestment flows were excluded.

The worked example assumes stable marks and no financing, tax, cash drag or price movement between legs. Those omissions do not change its accounting lesson: execution costs attach to transactions. They do limit using the example as a forecast of total implementation drag. Do not describe the gross traded fraction as a fund’s official turnover ratio.

Keep in the decision record

• Count both buy and sell notional for this workbench’s cost convention.
• Keep gross trading, net cash movement and one-sided replacement separate.
• Disclose the denominator before comparing reported turnover figures.

Source notes

1. SEC — Form N-1A informational version, portfolio turnover instructions
2. SEC — Tailored Shareholder Report Common Issues

Sources inform the definitions and limitations. Scenario inputs and arithmetic are publication illustrations, not extracted market observations. Access checks are dated in the source inventory.

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